Recently, attention has been paid to electric double layer capacitors since the capacitors, out of various capacitors, have a large capacity. For example, any capacitor is widely used as a memory backup for electrical equipment. In recent years, in this use manner, the use of an electric double layer capacitor has been promoted. Furthermore, the use thereof is expected for automobiles, such as hybrid cars and fueled vehicles.
Electric double layer capacitors are classified into button-shaped, cylindrical, rectangular, and other types, and capacitors of various types are known. The button-shaped capacitor is produced, for example, by preparing a pair of polarizable electrodes in each of which an activated carbon electrode is set on a current collector, arranging a separator therebetween to form an electric double layer capacitor element, packing the element together with an electrolyte into a metallic case, and sealing up the case with an opening-sealing material and a gasket for insulating the two from each other. The cylindrical capacitor is produced by stacking such paired polarizable electrodes and a separator onto each other, winding the workpiece to form an electric double layer capacitor element, impregnating this element with an electrolytic solution, packing the element into an Al case, and sealing up the case with an opening-sealing material. About the rectangular capacitor also, the basic structure thereof is similar to that of the button-shaped or cylindrical capacitor.
The electric double layer capacitors used for memory backups, automobiles and others are desired to be made higher in capacity and others. In other words, the capacitors are desired to be made higher in capacity per unit volume, and lower in internal resistance. For this purpose, various suggestions are made about a current collector that constitutes each of their electrodes. As the current collector, known are, for example, a current collector using a foil-piece, network-form, or punched metal of Al, stainless steel or some other metal (Patent Literature 1), a current collector wherein a mat made of a stainless steel fiber is electrically welded to a stainless steel foil piece (Patent Literature 2), a current collector using a porous body having a lath plate structure made of at least one metal of tantalum, Al and titanium (Patent Literature 3), and other current collectors.